1. Field of the Invention
The present invention relates to carbon nanotube-based devices and methods for making such carbon nanotube-based devices.
2. Description of the Related Art
Carbon nanotubes are very small tube-shaped structures essentially having the composition of a graphite sheet rolled into a tube. Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes have very good electrical conductance due to their structure. They are also chemically stable, and have very small diameters (less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that carbon nanotubes can play an important role in fields such as microscopic electronics, materials science, biology and chemistry.
Although carbon nanotubes promise to have a wide range of applications, better control is needed over the building and organization of nanotube-based architectures. Normally, the orientation of growing nanotubes is controlled such that the nanotubes are rectilinear and parallel to each other. Chemical vapor deposition has been used to produce nanotubes vertically aligned on catalyst-printed substrates. A method for controlling the growth of aligned nanotubes in several directions on a substrate in a single process is reported in an article by B. Q. Wei et al. entitled “Organized Assembly of Carbon Nanotubes” (Nature Vol. 416, Apr. 4, 2002, pp. 495-496).
Another method for controlling the growth of carbon nanotubes by means of electric fields is reported in an article by Yuegang Zhang et al. entitled “Electric-Field-Directed Growth of Aligned Single-Walled Carbon Nanotubes” (Applied Physics Letters, Vol. 79, Nov. 5, 2001, pp. 19).
However, carbon nanotubes of all the carbon nanotube based structures obtained by the above-mentioned methods are aligned along a linear direction, and/or extend perpendicularly from the substrates. Furthermore, the method of using an external electric field to control a direction of growth of the carbon nanotubes is difficult to apply in generating localized complicated structures with plural orientations of the carbon nanotubes. Accordingly, the range of diversity of different kinds of carbon nanotube-based devices is limited.
What is needed, therefore, is a carbon nanotube-based device with plural orientations of the carbon nanotubes and a method for making the such device.